1. Field
Exemplary embodiments relate to an electro-acoustic transducer, and more particularly, to a micromachined electro-acoustic transducer.
2. Description of the Related Art
Electro-acoustic transducers are devices that convert electric energy to acoustic energy or vice versa and may include ultrasonic transducers and microphones. Micromachined electro-acoustic transducers are transducers that use a micro-electro-mechanical system (MEMS). A typical example of a micromachined electro-acoustic transducer is a micromachined ultrasonic transducer (MUT), which is a device that converts an electric signal to an ultrasonic signal or vice versa. An MUT may be classified into a piezoelectric MUT (pMUT), a capacitive MUT (cMUT), and a magnetic MUT (mMUT), based on its converting method.
A pMUT has been mainly used in the past. Recently, the cMUT is increasingly under development because of its merits, such as a capability of transmitting/receiving a broadband signal, a conduciveness to mass production using a semiconductor process, and a capability of integration with an electric circuit. Accordingly, a cMUT is widely used in medical image diagnosis devices or sensors.
Recently, as a demand for various types of ultrasound signal acquisition methods and resulting images such as a B-mode image, a Doppler image, a harmonic image, and a photoacoustic image, which are obtainable for use in an ultrasound diagnosis, increases, ultrasound equipment having broadband characteristics is increasingly under development. Further, on order to cover diagnosis of various organs having different sizes and depths such as the abdomen, the heart, and the thyroid gland, the development of ultrasound equipment having a broadband characteristic is essential. Compared to a general piezoelectric ultrasonic transducer, although a cMUT is capable of transceiving broadband signals, it has a limit in receiving the overall frequency band. Accordingly, methods of embodying broadband by combining cells having different resonant frequencies are being developed.